Well starting from scratch for a rewrite is generally a bad idea. I'm more a fan of incremental re-wrties. But I have code bases I have been working on for years with tens of thousands of lines where basically the entire thing gets rewritten ever 18 months or so, a bit at a time.

Isn't your example proof of the benefit of pragmatic coding? Synapse is actually serving users right now. Dendrite sounds like a "better design" which is stuck in purgatory.